This invention relates to a drillpipe assembly for use in the logging of a borehole that perforates a geological formation. The invention also relates to a method of deploying a logging tool for the logging of such a borehole.
The logging of boreholes is technique well known in the oil and gas industries. The advantages of such an activity are well known to those skilled in the art of oil and gas production.
When a borehole is drilled, it is seldom smooth and regular. Sections of the borehole sometimes cave in. Sometimes there are other sections of rock, in particular shales and clays, that squeeze into the borehole as a result of pressure exerted by overlying strata.
Traditionally, borehole logging has involved the use of a so-called wireline logging tool. The wireline logging tool is lowered on a wireline or pushed on drillpipe into the borehole to a downhole, logging location. The wireline logging tool is connected by a wireline to eg. data processing and recording apparatus at a surface location external of the borehole.
Wireline logging tools are of comparatively large diameter. Consequently it is difficult to push or lower a wireline logging tool into a borehole having caved in or squeezed sections as aforesaid.
In recent years it has become known to employ, for the logging of boreholes, a so-called compact battery/memory logging tool. This logging tool typically is of considerably less diameter than a wireline logging tool. It includes a self-contained power supply in the form of a series of batteries; and one or more memory devices, whose function is to record data logged by the logging tool.
Battery memory logging tools in many circumstances offer advantages over traditional, wireline tools.
The deployment of a battery memory logging tool has hitherto involved securing the tool to the end of a length of drillpipe, such that the logging tool protrudes from the end of the drillpipe; and then driving the tool and drillpipe combination down the borehole, successively adding further lengths of drillpipe at the surface, and forcing the drillpipe assembly into the borehole.
This technique has been necessary because it is important for the logging tool to log the borehole in its openhole condition, ie. when there is no casing or other liner that would interfere with the accuracy of data detection and recording by the tool. Therefore it has hitherto proved necessary to advance the logging tool along the whole length of the borehole to its furthest extremity or total depth (xe2x80x9cTDxe2x80x9d), with the logging tool protruding from the forwardmost joint of the drillpipe.
The caved in and squeezed sections of the borehole present particular hazards to the deployment of battery memory logging tools in this fashion. The protruding tool can snag and become damaged on such formations.
The caved in and squeezed sections of borehole are particularly prevalent in wells that are significantly deviated from the vertical or horizontal; and also in curved wells.
Furthermore, the likelihood of jamming or damaging a battery memory logging tool during its deployment means that logging engineers tend to deploy the tools at a comparatively slow rate, so as to minimise the risk of damage to the tools. Since rig time is often expensive oil and gas production companies wish to maximise the amount of time spent logging a borehole, as compared with deploying the logging tool. As a result there is scope for improvements in the efficiency of logging tool deployment operations.
It is an aim of the invention to overcome or at least ameliorate one or more of the disadvantages of the prior art apparatuses and methods.
According to a first aspect of the invention, there is provided a drillpipe assembly comprising a drillpipe having secured at a downhole end thereof a delatchable latching sub containing an extendible running sub supporting a logging tool, the running sub being moveable between a first, retracted position, in which it supports the logging tool within one or more stands of drillpipe; and a second, extended position in which it supports the logging tool protruding from the drillpipe, the latching sub, when latched, retaining the running sub in its first position and the latching sub permitting extending of the running sub when delatched.
The use of an apparatus that is capable of holding the logging tool retracted within a joint of drillpipe during deployment, and subsequently extending the logging tool to protrude from the drillpipe, allows deployment of the logging tool without fear that the tool will become snagged, damaged or broken off.
Furthermore, the ability to deploy the logging tool in a retracted condition allows rapid deployment over most of the travel of the logging tool along the borehole. Only at the extreme end of its travel, near the TD of the well, is it necessary to complete deployment of the logging tool at a slow rate.
As a result, the overall logging tool deployment time is significantly reduced. This in turn minimises the amount of rig time that is not used for logging operations.
In a preferred embodiment of the invention, the logging tool is a compact diameter battery memory tool. However, within the scope of the invention it is possible to devise a drillpipe assembly intended to deploy larger diameter tools than the known compact battery memory tools.
Preferably the assembly of the invention includes an hydraulic actuator for extending the running sub.
More specifically, the hydraulic actuator preferably includes one or more seals moveably sealingly interconnecting an outer periphery of the running sub and an inner wall of a drillpipe stand, whereby fluid pressure in the drillpipe acting on one side of a said seal tends to drive the running sub along the drillpipe.
Clearly while the latching sub is latched, there is resistance to movement of the running sub; but when the latching sub is delatched the hydraulic pressure acting on the seals of the running sub conveniently drives the running sub to extend from the downhole end of the drillpipe assembly.
Conveniently the or each said seal is a flexible cup seal sealingly secured to the running sub and in slideable sealing contact with the said drillpipe stand inner wall.
Flexible cup seals (also known as swab cups) are advantageously effective in providing the necessary sealing qualities. Furthermore flexible cup seals are able to accommodate changes in diameter in the internal wall of the drillpipe stand with which they engage. Consequently there is no need to maintain a constant inner diameter of the drillpipe through which the running sub is driveable.
Preferably the running sub defines a closeable fluid flow path bypassing the or each said seal, such that closing of the said path causes fluid pressure in the drillpipe to act on the or each said seal.
In preferred embodiments of the invention the drillpipe assembly includes a pumpable messenger member moveably disposed in the drillpipe. Conveniently the said fluid flow path is closeable by the messenger member.
More specifically, the running sub includes a hollow conduit that is open at either end and defines the aforesaid fluid flow path bypassing the or each said seal. The messenger member includes a sealing member and is insertable into the said conduit at a location uphole of the or each said seal to prevent the flow of fluid via the conduit, thereby closing the said fluid flow path.
Consequently the use of a running sub that includes a fluid flow path; together with a messenger member that is capable of closing the fluid flow path when inserted into the running sub, is an advantageously simple and reliable method of permitting hydraulic pressure in the drillpipe uphole of the running sub selectively to act on the seals thereof to drive the running sub forwardly of the drillpipe itself.
In a preferred embodiment of the invention the messenger member includes a shield that is moveable between a first position in which it obscures the sealing member and a second position in which the sealing member is exposed for sealing of the conduit uphole of the or each said seal of the running sub.
This arrangement advantageously ensures that the sealing member remains in good condition while the messenger member travels along the drillpipe.
Preferably the latching sub includes a member that is capable of moving the shield to its second position on insertion of the messenger member into the conduit.
This feature advantageously causes the shield to expose the sealing member when the messenger member is correctly inserted into the conduit defined in the running sub.
Preferably the latching sub includes one or more arms each pivotably secured thereto so as to be moveable between a first position, protruding outwardly from the latching sub; and a second position that is retracted relative to the first position, the drillpipe adjacent the latching sub including an abutment with which each said arm is engageable, when occupying its first position, to prevent movement of the latching sub in a downhole direction, the abutment defining a clearance through which the latching sub is moveable in a downhole direction when the or each said arm occupies its second position.
Consequently the latching sub is latched, to secure the running sub such that the logging tool is within the drillpipe, while the or each said arm occupies its first, comparatively extended position.
Once the arms retract relative to the remainder of the latching sub, the effective diameter of the latching sub is sufficiently small as to permit its passage through the clearance.
Preferably the drillpipe assembly includes a resiliently deformable biasser acting, between the or each said arm and a member that is fixed relative to the latching sub, to bias the or each said arm to its first position.
It is also preferable that the or each said arm includes a follower portion protruding into a hollow, interior part of the latching sub, the messenger member being receivable in the said hollow interior and including a surface engageable with the follower portion, on insertion of the messenger member into the hollow interior, whereby to move the or each arm to its second position.
Consequently when the messenger member engages the latching sub, the follower portion moves the or each said arm to its second position to permit delatching of the latching sub and its passage through the aforesaid clearance.
Thus the messenger member preferably carries out two functions, namely that of closing the bypass flow path so that fluid pressure acts to drive the running sub to extend the logging tool; and that of delatching the latching sub.
If desired, during design of the latching sub and messenger member the length of the messenger member may be adjusted in order to determine the order in which the aforesaid functions take place.
Preferably the latching sub and the messenger include a detent arrangement for securing the messenger member to the latching sub following engagement therebetween.
The detent arrangement ensures that, following delatching of the latching sub, the messenger member remains attached thereto. This in turn ensures that the messenger member continues effectively to close the bypass fluid flow path, throughout the deployment of the logging tool.
In a particularly preferred embodiment, the detent arrangement includes a moveable barb that is resiliently biassed to protrude into the hollow interior of the latching sub; and a notch, of complementary profile to the barb, formed in the messenger member.
This detent arrangement is advantageously reliable.
It is of course within the scope of the invention for the barb, or a functionally equivalent device, to be formed on the messenger member; and the notch to be part of the latching sub.
Conveniently the messenger member includes a cylindrical member of smaller diameter than the internal diameter of the drillpipe, the cylindrical member being encircled by one or more flexible cup seals.
This arrangement ensures that the messenger member can travel along the length of the drillpipe even if the internal diameter of the drillpipe varies from place to place.
The use of flexible cup seals additionally advantageously ensures that the messenger member is self-centring in the drillpipe. This is beneficial particularly to ensure correct engagement of the messenger member with the latching sub, in a manner described hereinbelow.
It is also preferable that the cylindrical member forming part of the messenger member is hollow and closed at at least one end.
Use of a hollow cylindrical member means that the messenger member as a whole can be manufactured as light as possible, thereby reducing the energy required to pump a messenger member along the drillpipe. Clearly however at least one end of the messenger member must be closed otherwise the flexible cup seals would be ineffective in providing pumped driving of the messenger member.
The drillpipe assembly of the invention preferably includes a mule shoe landing sub at its furthest downhole extremity, the mule shoe landing sub including an hydraulic signal generator for generating a signal, that is detectable at surface level, indicative of deployment of the logging tool.
More preferably, the mule shoe landing sub includes a mule shoe drillpipe stand having a first valve port formed therein providing fluid communication between the interior and exterior of the mule shoe drillpipe stand and being closed by a hollow valve sleeve slidingly sealingly engaged with a surface of the mule shoe drillpipe stand, the running sub preferably including a member engageable, following extension of the running sub from the latching subs with the valve sleeve, to move it to an open position of the first valve port.
Thus the running sub advantageously serves to activate a signal generator that indicates at a surface location that the logging tool that is attached to the running sub has been deployed to the TD of the well.
Conveniently the mule shoe landing sub includes a resiliently deformable biasser biassing the valve sleeve to the closed position of the first valve port.
In a particularly preferred embodiment the biasser is a spring that forces a sleeve to cover and hence close the valve port.
The biasser applies a bias pressure such as but not limited to 500 psi, such that a substantial pressure is needed to open the said first valve port. This in turn assures firstly that the mule shoe landing sub does not send a false deployment signal; and secondly that the deployment signal is easily detected, in a manner described below, at a surface location external of the well.
Conveniently the mule shoe drillpipe stand includes a second valve port located downhole of the first valve port and normally closed by the valve sleeve, whereby on further movement of the valve sleeve, away from the normally closed position of the first valve port, the second valve port opens after opening of the first valve port.
This arrangement permits the generation of successive deployment signals, thereby providing a surface-located operator with confirmation of correct deployment of the logging tool.
A preferred arrangement of the second valve port is one in which the mule shoe landing sub includes an abutment preventing movement of the valve sleeve to open the second valve port, the abutment being retained relative to the mule shoe landing sub by one or more shear fasteners that on shearing permit opening of the second valve port.
In a particularly preferred embodiment, the drillpipe pressure necessary to shear the shear fastener is greater than the pressure necessary to overcome the biasser that maintains the first valve port in its normally closed condition. This arrangement provides advantages in terms of the reading of the deployment signal at a surface location.
The invention is also considered to reside in an assembly as aforesaid, when inserted in a wellbore that includes an openhole section downhole of the assembly of the invention.
This arrangement of course allows accurate logging of the wellbore, since logging tools are designed to log openhole wells.
A further, optional feature of the drillpipe assembly of the invention is a hollow float valve sub defining a fluid flow path and located uphole of the latching sub, the float valve sub including two normally closed non-return valves that each prevent fluid overpressure in the drillpipe assembly transmitting to the surface, each said non-return valve being openable by a pumpable messenger passing in the downhole direction through the float valve sub.
This arrangement advantageously prevents fluid overpressure downhole of the float valve sub from transmitting to the surface. In other words, the float valve sub prevents downhole overpressure from blowing components of the drill string, together with the drilling mud, out of the open end of the wellbore at the surface location.
In a particularly preferred embodiment of the invention, the two non-return valves of the float valve sub are spaced apart from one another in the elongate direction of the float valve sub by a length greater than the length of a said messenger member inserted into the drillpipe assembly.
This ensures that even as the messenger member passes through the float valve sub, at no time are both the valve members of the float valve sub open.
According to a second aspect of the invention there is provided a kit of parts, for forming a drillpipe assembly according to any preceding claim, comprising:
a plurality of joints of drillpipe;
a delatchable latching sub capable of containing an extendible running sub;
a running sub that is containable in the latching sub; and
a battery/memory logging tool.
Optionally the kit may further include one or more components selected from:
a pumpable messenger;
a mule shoe landing sub; and/or
a float valve sub.
A kit according to the second aspect of the invention is readily dismantleable for transportation. Furthermore, the presence of a number of drillpipe joints means that the length of the drillpipe assembly may readily be adjusted to suit the depth of the well to be logged.
According to a third aspect of the invention there is provided a method of deploying a battery/memory logging tool in a wellbore, the method comprising the steps of:
(i) securing a delatchable latching sub in a drillpipe assembly;
(ii) supporting a battery/memory logging tool on an hydraulically pumpable running sub that is temporarily latchable in the latching sub;
(iii) latching the running sub in the latching sub so that the logging tool lies within a length of drillpipe;
(iv) running in a plurality of stands of drillpipe above the latching sub, until the drillpipe is of a preferred length;
(v) pumping a pumpable messenger member down the drillpipe to de-latch the latching sub and release the running sub, having the logging tool supported thereon, therefrom; and
(vi) when the logging tool reaches an openhole location, commencing logging with the logging tool.
The method of the invention advantageously permits the rapid deployment of a logging tool, without any risk of the tool becoming snagged, damaged or broken as a result of encountering the aforementioned well defects.
Preferably the method includes the further step of, before securing the latching sub, (vi) securing a mule shoe landing sub at the downhole end of the drillpipe assembly; and further including the step of, after release of the running sub, (vii) engaging the running sub and the mule shoe landing sub with one another to generate one or more hydraulic signals indicative of deployment of the logging tool.
This aspect of the method of the invention ensures the generation of a positive signal indicative of correct deployment of the logging tool.
Conveniently the method includes the sub steps of, after the step (iv) of running in the plurality of stands of drillpipe, (iv)(a) withdrawing the drillpipe from the wellbore by one or more joints; and (iv)(b) removing the withdrawn stands of drillpipe thereby creating an openhole bore before releasing the logging tool.
This series of substeps ensures that a portion of the well is in the openhole condition, thereby permitting commencement of logging operations.
Following releasing of the running sub from the latching sub, the method of the invention optionally also includes the steps of (viii) withdrawing and removing each successive stand of drillpipe from the surface of the wellbore, thereby withdrawing the drillpipe assembly; and (ix) during step (viii) logging the openhole bore.
Thus the method of logging the bore inherently includes gradual removal of the components of the assembly from the bore while logging takes place.
Conveniently the step (iv) of running in a plurality of stands of drillpipe includes the further sub-steps of (iv)(c) running in the majority of the stands at a first, comparatively high speed; and, when the downhole end of the drillpipe assembly approaches the Total Depth (TD) of the well,
(iv)(d) running in the remainder of the stands at a second, lower speed.
This aspect of the method permits the bulk of the deployment operation to take place at a high speed. The speed of deployment only needs to be reduced as the logging tool approaches the TD of the well.
Consequently, the method of the invention makes efficient use of the rig times.
More specifically, the step (v) of the method of the invention preferably includes the substeps of (v)(a) engaging together the messenger member and an actuator for a moveable detent member to cause disengagement of the detent member from a further member to permit releasing of the running sub; and
(v)(b) closing a bypass flow of fluid whereby to divert the flow to pump the running sub in a downhole direction.
This provides a conveniently switchable, efficient method of driving or pumping the running sub along the drillpipe, for purposes of deploying the logging tool.
Preferably the substeps (v)(a) and (v)(b) occur substantially simultaneously.
As noted hereinabove, the length of the messenger member may if desired be chosen to dictate the time lag between the two said steps.